A method of the above kind for operating an internal combustion engine is disclosed in United States patent application publication no. US 2006/0157006 A1 (now U.S. Pat. No. 7,325,528) which is incorporated herein by reference and is assigned to the same assignee as the present application.
U.S. Pat. No. 5,901,673 discloses a two-stroke engine wherein fuel is injected into the combustion chamber for each crankshaft revolution in the region of bottom dead center of the piston and the air/fuel mixture, which is formed in the combustion chamber, is ignited in the region of the top dead center of the piston.
United States patent application publication no. US 2006/0157006 A1 (now U.S. Pat. No. 7,325,528) discloses controlling a two-stroke engine in at least one operating state so that the number of combustions is less than the number of revolutions of the crankshaft in the same time interval.
To limit the rpm of an internal combustion engine, U.S. Pat. No. 6,880,525 discloses holding the ignition switch open when exceeding an end rpm in order to suppress an ignition spark over at least one crankshaft revolution. The suppression of the ignition spark is intended to prevent a combustion in the next engine cycle. In this way, a reduction of the rpm can be reached so that the rpm cannot increase uncontrolled beyond a highest rpm.
It has been shown that in internal combustion engines controlled in this manner, a large increase of the rpm from the full load rpm can occur when the load is suddenly reduced. This can, for example, take place in a brushcutter when the filament tears. The sudden uncontrolled increase of the rpm leads to a high load on the component. It has furthermore been shown that the exhaust gas values deteriorate greatly with an uncontrolled increase of the rpm.